From 35cda8872e693b513fb09b2d26b561a9a039f2ae Mon Sep 17 00:00:00 2001
From: q66 <daniel@octaforge.org>
Date: Sat, 18 Mar 2017 18:34:13 +0100
Subject: [PATCH] add a thread pool impl

---
 ostd/concurrency.hh |   1 -
 ostd/thread_pool.hh | 111 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 111 insertions(+), 1 deletion(-)
 create mode 100644 ostd/thread_pool.hh

diff --git a/ostd/concurrency.hh b/ostd/concurrency.hh
index e706211..d27db6c 100644
--- a/ostd/concurrency.hh
+++ b/ostd/concurrency.hh
@@ -6,7 +6,6 @@
 #ifndef OSTD_CONCURRENCY_HH
 #define OSTD_CONCURRENCY_HH
 
-#include <stdio.h>
 #include <thread>
 #include <utility>
 
diff --git a/ostd/thread_pool.hh b/ostd/thread_pool.hh
new file mode 100644
index 0000000..86fb43b
--- /dev/null
+++ b/ostd/thread_pool.hh
@@ -0,0 +1,111 @@
+/* A thread pool that can be used standalone or within a more elaborate module.
+ *
+ * This file is part of OctaSTD. See COPYING.md for futher information.
+ */
+
+#ifndef OSTD_THREAD_POOL_HH
+#define OSTD_THREAD_POOL_HH
+
+#include <type_traits>
+#include <functional>
+#include <utility>
+#include <vector>
+#include <queue>
+#include <thread>
+#include <future>
+#include <mutex>
+#include <condition_variable>
+
+namespace ostd {
+
+struct thread_pool {
+    void start(size_t size = std::thread::hardware_concurrency()) {
+        p_running = true;
+        auto tf = [this]() {
+            thread_run();
+        };
+        for (size_t i = 0; i < size; ++i) {
+            std::thread tid{tf};
+            if (!tid.joinable()) {
+                throw std::runtime_error{"thread_pool worker failed"};
+            }
+            p_thrs.push_back(std::move(tid));
+        }
+    }
+
+    ~thread_pool() {
+        destroy();
+    }
+
+    void destroy() {
+        std::unique_lock<std::mutex> l{p_lock};
+        if (!p_running) {
+            return;
+        }
+        p_running = false;
+        l.unlock();
+        p_cond.notify_all();
+        for (auto &tid: p_thrs) {
+            tid.join();
+            p_cond.notify_all();
+        }
+    }
+
+    template<typename F, typename ...A>
+    auto push(F &&func, A &&...args) -> std::result_of_t<F(A...)> {
+        using R = std::result_of_t<F(A...)>;
+        if constexpr(std::is_same_v<R, void>) {
+            /* void-returning funcs return void */
+            std::unique_lock<std::mutex> l{p_lock};
+            if (!p_running) {
+                throw std::runtime_error{"push on stopped thread_pool"};
+            }
+            p_tasks.push(
+                std::bind(std::forward<F>(func), std::forward<A>(args)...)
+            );
+            p_cond.notify_one();
+        } else {
+            /* non-void-returning funcs return a future */
+            std::packaged_task<R> t{
+                std::bind(std::forward<F>(func), std::forward<A>(args)...)
+            };
+            auto ret = t.get_future();
+            std::unique_lock<std::mutex> l{p_lock};
+            if (!p_running) {
+                throw std::runtime_error{"push on stopped thread_pool"};
+            }
+            p_tasks.emplace([t = std::move(t)]() {
+                t();
+            });
+            p_cond.notify_one();
+            return ret;
+        }
+    }
+
+private:
+    void thread_run() {
+        for (;;) {
+            std::unique_lock<std::mutex> l{p_lock};
+            while (p_running && p_tasks.empty()) {
+                p_cond.wait(l);
+            }
+            if (!p_running && p_tasks.empty()) {
+                return;
+            }
+            auto t = std::move(p_tasks.front());
+            p_tasks.pop();
+            l.unlock();
+            t();
+        }
+    }
+
+    std::condition_variable p_cond;
+    std::mutex p_lock;
+    std::vector<std::thread> p_thrs;
+    std::queue<std::function<void()>> p_tasks;
+    bool p_running = false;
+};
+
+} /* namespace ostd */
+
+#endif